Electric robot for use in a hazardous location

ABSTRACT

A multi-axis electric spraying robot adapted for use in a hazardous environment includes a base having a first pressurized compartment and an arm assembly having a second pressurized compartment in which compartments electric motors are respectively located. The arm assembly is supported for movement on the base at one end thereof. The arm assembly includes a wrist adapted for connecting the opposite end of the arm assembly with a spraying tool. One electric motor is provided to drive each axis. The compartments are pressurized to prevent flammable gases or vapors from entering the first and second compartments during operation of the robot.

This is a continuation of application Ser. No. 07/370,123, filed on Jun.20, 1989, now U.S. Pat. No. 4,984,745, which is a continuation of Ser.No. 07/183,452, filed Apr. 14, 1989; now abandoned; which is acontinuation of Ser. No. 06/928,641, filed Nov. 6, 1986, abandoned;which is a continuation of Ser. No. 06/692,996, filed Jan. 22, 1985,abandoned.

TECHNICAL FIELD

This invention relates to electrically driven robots adapted for use inhazardous ambients and, in particular, electrically driven robots whichcan operate in an environment containing flammable gases or vapors.

BACKGROUND ART

Many spray painting machines have been introduced to paint mass-produceditems such as automotive bodies. Such paint spraying machines havetypically been limited in their use in that they must be backed up byhuman operators, who must touch up areas missed by the machines. Suchmachines also tend to be wasteful of paint and are only designed topaint with horizontal and/or vertical paths on a reciprocator system.Coating an object fully, especially if it has complex contours, requiresmovements in depth as well as lateral movements. The use of a wrist issignificant in that it is often necessary for an operator to angle apaint spray gun in a particular manner to deposit paint on a heavilycontoured surface.

Many of the prior art spray painting machines include a battery of sprayguns fed from large capacity, centralized paint reservoirs which manageto paint a large percentage of the exterior surface to be covered. Lessaccessible areas, such as wheel arches, the interiors of the trunk orengine compartment and door edges had to be painted by operators wholooked for unpainted areas as the car body left the automatic painter.

Numerous prior art patents disclose painting machines includingelectrical painting apparatus such as the U.S. Pat. No. to Chapman2,858,947; the U.S. Pat. No. to Shelley et al 3,007,097; the U.S. Pat.No. to Pierson et al 3,481,499; the U.S. Pat. No. to Richter 4,030,617;the U.S. Pat. No. to Yoshio 4,113,115; the U.S. Pat. No. to Burns et al4,196,049; the U.S. Pat. Nos. to Shum 4,398,863 and 4,407,625; the U.S.Pat. No. to Jacot-Descombes et al 4,424,472 and the U.S. Pat. No. toGorman 4,424,473. The U.S. Pat. Nos. to Pollard 2,213,108 and 2,286,571both disclose electrical robots for paint spraying. The U.S. Pat. No. toStricker 4,170,751 likewise discloses an electric apparatus associatedwith paint spraying robots.

There are many reasons for using spraying robots to provide high-qualitypainted finishes on a mass-produced item. Robots are desirable in thatthey are able to cope with the hostile painting environment; they allowthe painting process to proceed with less total energy being expended;and they improve paint quality which, in turn, will eventually result inreduced material and labor costs. The above advantages are particularlyimportant in painting car bodies where production rates are expected tobe high, and there is a relatively small amount of time available forthe paint to be applied and completed in not one, but several coats.

A spraying robot can also be used in the enameling and/or powdering ofsurfaces. For example, application of vitreous enamel to plasticbathtubs utilizes many of the same spray techniques as used in theapplication of paint to an automotive body.

Robots which have been used for spray painting comprise continuous pathmachines which emulate the action of a human operator. Such robots aretypically taught by having an expert painter lead each robot in itslearning mode through an actual paint job.

The average spray booth in the automotive industry has been standardizedto have a relatively small width. This small width restricts the sizeand movements of any robot which is to be used in such a spray booth.Redesigning the existing spray booth is cost prohibitive.

Because of the limited size available for a robot in a conventionalpaint spray booth, the use of a robot having electrical drives is, atfirst blush, desirable due to the cost advantage that small electricalrobots enjoy over small hydraulically-driven robots. Such costs not onlyinclude the cost of the robot, but also installation, maintenance andother operational expenses. However, in paint spraying and other similarapplications the environment favors the use of hydraulically orpneumatically driven equipment. Such environment presents an explosionhazard to electrical motors and the electrical robot must either beexplosion proof or intrinsically safe so as not to ignite thecombustible environment. A hydraulically-driven robot does not utilizethe amount of electrical energy typically sufficient to ignite theexplosive fuel-air mixture.

Electrical equipment which is to be located in areas classified as"hazardous" (i.e. a Class 1, Division 1 location) by Article 500 of NFPA70, Natural Electrical Code, either must be placed in pressurizedcontainers or must be made explosion proof. If this is done the areaimmediately around the electrical equipment is no longer classified as aClass 1, Division 1 location, but rather a Class 1, Division 2 locationwherein only the location adjacent the enclosure or explosion proofcontainer contains the ignitable concentration of flammable gases orvapors under normal operating conditions. The pressurization of theenclosure entails supplying the enclosure with clean air or an inert gaswith or without continuous flow at sufficient pressure to prevent theentrance of combustible gases or vapors which might occasionally becommunicated into the enclosure. If the enclosure is maintained under apositive pressure of at least 25 pascals (0.1 inches of water) when theelectric equipment is energized, the risk of an explosion in the"hazardous" environment is substantially eliminated.

One way of complying with the above standard is to make the containersfor the equipment, such as motors, explosion-proof. However, the use ofexplosion-proof motors not only increases the cost of the motors, butalso increases the weight and size of the robot. Also, the use ofexplosion-proof motors necessitates the use of explosion-proof cables.Such cables not only are more costly and heavier, but also are moreinflexible and unwieldly. Such explosion-proof motors and cables alsotake up valuable space in or on the robot and, consequently, in thepaint spray booth.

DISCLOSURE OF THE INVENTION

An object of the present invention is to provide an improvedelectrically driven robot adapted for use in a hazardous environment.

Another object of the present invention is to provide a relativelycompact robot adapted for use in a hazardous environment and whichincludes a pair of pressurized compartments for housing electric motorstherein.

Yet still another object of the present invention is to provide arelatively compact and inexpensive electrically driven robot adapted foruse in hazardous environments, including a base, an arm assembly andfirst and second drive systems including first and second electricmotors, respectively, and wherein at least one electric motor is locatedin a first pressurized compartment located in the base and at least oneelectric motor is located in a second pressurized compartment located inthe arm assembly.

In carrying out the above objects and other objects of the presentinvention an electrically driven robot constructed in accordance withthe present invention includes a base having a first pressurizedcompartment contained therein, and an arm assembly having a secondpressurized compartment contained therein. The arm assembly is supportedfor movement on the base at one end thereof. The arm assembly includes awrist adapted for connecting its opposite end with a fluid deliverytool. The robot also includes first and second drive systems. The firstdrive system includes at least one electric motor located in the firstpressurized compartment to drive the arm assembly. The second drivesystem includes at least one electric motor located in the secondpressurized compartment to drive the wrist.

Preferably, the electric motors comprise brushless servo motors commonlyknown as brushless D.C. motors or AC servo motors.

Also, preferably, the robot includes cables which are housed in apressurized conduit attached to the outer surface of the base. Thecables are electrically coupled to the electric motors and adapted to becoupled to a robot controller. The conduit is in fluid communicationwith first and second pressurized compartments. Consequently, the cablesmay comprise regular duty cables rather than heavy duty, explosion-proofcables.

Pressurizing means includes a pressure regulator that provides apositive pressure in the first and second compartments and also,preferably, in the conduit.

An electric spraying robot constructed in this fashion is not onlyrelatively small and lightweight, but also less costly than comparablehydraulically-driven robots. The electric spraying robot also includesregular duty cables and does not necessitate the use of heavy duty,explosion-proof cables and their attendant disadvantages. The use of apair of pressurized compartments, one of which is located in the armassembly, minimizes the amount of gearing or other mechanisms requiredtherein to transfer the rotary motion of the drive motors to a wristmechanism mounted on the free end of the arm assembly.

Other advantages of the present invention will be readily appreciated asthe same becomes better understood by reference to the followingdetailed description when considered in connection with the accompanyingdrawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a perspective view of an electric spraying robot constructedin accordance with the present invention;

FIG. 2 is a side elevational view of a lower base section of the robotof FIG. 1;

FIG. 3 is a broken-away, side elevational view of the lower section ofFIG. 2 illustrating various components contained therein;

FIG. 4 is a side elevational view of the various cables of the robotwherein the outer housing structure of the robot is indicated by phantomlines;

FIG. 5 is an enlarged view of a portion of FIG. 4 illustrating thesealing mechanism between the upper and lower sections of the base;

FIG. 6 is a top plan view of the cables of FIG. 4 wherein the variousother components of the robot are illustrated in phantom; and

FIG. 7 is a broken-away, top plan view of an inner arm of the robot.

BEST MODE FOR CARRYING OUT THE INVENTION

Referring now to FIG. 1 there is illustrated a paint spray robotconstructed in accordance with the present invention and collectivelyindicated by reference numeral 10. The spray robot 10 includes a base,generally indicated at 12 having an upper base section 14 and a lowerbase section 16. The upper base section 14 is rotatable with respect tothe stationary lower base section 16. The robot 10 also includes an armassembly, generally indicated at 18, including an inner arm 20 pivotallyconnected to the upper base section 14 at one end thereof and to anouter arm 22 at its opposite end thereof. A wrist or wrist mechanism 24is connected at the free end of the outer arm 22 and preferablycomprises a three-axis wrist mechanism. The wrist mechanism 24 isadapted to hold a spraying tool, such as a paint spray gun at its freeend thereof.

As described in greater detail hereinafter, the robot 10 includes an airsystem for pressurizing the base 12 and the arm assembly 18 so thatnon-sparking electric motors can be located within pressurizedcompartments located therein without requiring the use ofexplosion-proof electric motors. Also, because the electric motors fordriving the wrist mechanism 24 are located in the arm assembly 18, andnot the base 12, the amount of gearing required to interconnect theelectric motors with the wrist mechanism 24 is substantially reduced. Itis obvious that the second pressurized compartment can be located withinthe inner arm 20 as described herein, or within the outer arm 22 ifdesired.

As illustrated in FIG. 1, the robot 10 is adapted for use in a hazardousambient or environment such as within a paint spray booth, a wall ofwhich is illustrated at 26. The lower base section 16 is adjustablymounted on the floor 29 of the paint spray booth by leveling jackassemblies 31 located at each lower corner of the lower base section 16,as best shown in FIG. 2.

The area within the paint spray booth is an area where flammable gasesor vapors may be present in the air in concentrations sufficient for thelocation to be classified as hazardous as defined by Article 500 of theNFPA 70, National Electrical Code. Such an environment may present anexplosion or fire hazard arising from the highly flammable nature of theexplosive solvent-air mixture contained therewithin.

Power and control signals for the robot 10 are carried by cables (notshown) which extend from a robot controller 28 located outside the paintspray booth. A pressurized conduit 30 houses the cables and is attachedto the lower base section 16. The lower base section 16 is adapted to beconnected to the pressurized conduit 30 by an adaptor plate 34 which, inturn, is mounted by bolts 32 on the front housing plate 36 of the lowerbase section 16. The cables contained in the conduit 30 extend through apassage 38 extending through the front wall 36 and are electricallyconnected or coupled to a terminal strip 40, as indicated in FIG. 4.

The adaptor plate 34 also includes an air inlet passage 42 which is influid communication with an air inlet tube 44, which also extendsthrough the wall 26 of the paint spray booth to permit relatively cleanair or inert gas to flow into the lower base section 16 from the ambientabout the paint spray booth.

After flowing through the air inlet passage 42 the air flows through atube 46 which is in fluid communication with an air pressure regulator48. The regulator 48 is mounted to an inner wall 50 of the lower basesection 16. The inner wall 50 defines an inner compartment 59 in thelower base section 16.

The pressure regulator 48 maintains the air pressure within a firstcompartment 52 within the lower base section 16 between predeterminedlimits. Also included within the first compartment 52 is a low pressureswitch 54 which indicates a pressure within the first compartment 52which is below the pressure that the pressure regulator 48 is designedto maintain. The pressure switch 54 is connected by means of a tube 56to the non-pressurized compartment 59 at a connector 58 as an access toa reference atmosperic pressure level. The pressure switch 54 is alsoconnected by a cable (not shown) to provide an alarm signal to the robotcontroller 28 to indicate that the robot 10 should be shut down due tothe low pressure in the first compartment 52.

A pair of umbrella vents 60 are also provided between the firstcompartment 52 and the inner compartment 59 at the inner wall 50 torelieve any excess pressure generated by the pressure regulator 48 abovea maximum predetermined limit. The umbrella vent 60 communicates theexcess pressure from the first compartment 52 to the inner compartment59.

The first compartment 52 is in fluid communication with a secondcompartment 62 formed in the upper base section 14 through an opening 64formed in the top wall of the lower base section 16. The opening 64 isaligned with an opening 66 formed in a drive plate 68 disposed betweenthe upper and lower base sections 14 and 16, respectively. In turn, theopening 66 is aligned with an opening 76, formed in a collar member 72which is bolted to the drive plate 68 by mounting bolts 74 as shown inFIG. 5. A circular seal 78 is provided between the collar member 72 andthe lower wall of the upper base section 14 to seal the compartment 62during relative rotation between the collar member 72 and its attachedplate 68 and the upper base section 14.

A directing means or mechanism, generally indicated at 80, is fixedlymounted to the collar member 72 and supports a plurality of regular dutycables 82 which are electrically connected in the lower compartment 52to the terminal strip 40. As shown in FIGS. 4 through 6, the cables 82are relatively flexible to permit the cables 82 to be formed into aribbon which, in turn, is bent along a relatively small radius ofcurvature. The cables are also flexible enough to permit flexing of theribbon during relative rotation between the collar member 72 and itsassociated directing mechanism 80 and the upper base section 14.

Each cable 82 includes three smaller cables 84 contained therein. Two ofthe smaller cables 84 are provided for each electric drive motor 86 ofan electric drive system mounted within the upper compartment 62. One ofthe smaller cables 84 provides the power signals and the other smallcable provides the control signals. Three drive motors 86 are located inthe upper compartment 62, one for each axis of rotation of the armassembly 18. Each drive motor preferably comprises a non-sparkingbrushless servo motor, commonly known as A.C. servo motor or brushlessD.C. motor.

Two of the cables 82 are routed and clamped to extend into a thirdpressurized compartment 88 contained in the inner arm 20, as best shownin FIGS. 6 and 7. The cables extend from the second pressurizedcompartment 62 into the third pressurized compartment 88 through anopening 90 formed in the outer wall 92 of the inner arm 20 and in theouter wall of the upper base section 14. The cables 82 are electricallyconnected to their respective electric motors 94 which are mountedwithin the third compartment 88. As shown in each of FIGS. 4 and 6, eachmotor 94 is smaller than each motor 86. Additional details of thespecific construction and operation of the ribbon of cables 82 are givenin co-pending U.S. patent application entitled "Robot With ImprovedCable Routing and Clamping", Attorney's Docket No. P-306 filed on evendate with the present application, now U.S. Pat. No. 4,659,279 andhaving the same Assignee and which is hereby incorporated by reference.

Drive shafts 96 of the motors 94 extend through inner walls 98 whichdefine the pressurized compartment 88 and are in driving engagement withtheir respective timing belts 100. Each timing belt 100 in turn, isoperatively connected to its respective gear mechanism for driving aseparate axis of the three-axis wrist mechanism 24 through hollowconcentric drive tubes.

A number of purging vents (not shown) are also provided in the innerwalls defining the compartments 52, 62 and 88 so that each of thecompartments can be provided with clean air or an inert gas atsufficient flow and pressure to reduce to an acceptably safe level theconcentration of any flammable gas or vapor which may have contaminatedany or all of the compartments. The pressure regulator 48 includes amanual bypass to allow this purging process when desired.

Also, appropriate seals may be provided between the various moving andnon-moving parts of the robot so that the positive pressure within thecompartments 52, 62 and 88 can be maintained, without an excess of airflow.

The above construction allows the use of a relatively small andinexpensive electric robot in a hazardous environment such as can befound in a conventional paint spray booth. The pressurized compartments52, 62 and 88 which either are in fluid communication with each other,or are individually pressurized, prevent flammable gases or vapors fromentering into the compartments which house electrical equipmentincluding the electric drive motors.

By providing the pressurized compartment 88 in the arm assembly 18, theamount of interconnecting gearing to drive the various axes of the wristmechanism 24 is substantially reduced. Also, the use of non-sparkingelectric motors in the various pressurized compartments eliminates theneed for relatively heavy and costly explosion-proof motors eitherwithin the robot 10 or attached on the exterior surface thereof. Afurther benefit of using the non-sparking electric motors within thepressurized compartments is that the cables providing the power andcontrol signals to the electric motors may comprise regular duty cablesand not heavy-duty explosion-proof cables which are not only morecostly, but also are relatively inflexible compared to regular dutycables.

The invention has been described in an illustrative manner and it is tobe understood that the terminology which has been used is intended to bein the nature of words of description rather than of limitation.

Obviously, many modifications and variations of the present inventionare possible in light of the above teachings. It is, therefore, to beunderstood that within the scope of the appended claims, the inventionmay be practiced otherwise than as specifically described.

What is claimed is:
 1. In an electric drive type robot of the typeintended for operation in an explosive atmosphere and including aplurality of electric drive motors and electric wiring for supplyingelectrical power to said motors, the improvement of antiexplosion meansfor preventing explosion of the explosive atmosphere by said electricdrive motors and said electric wiring, said antiexplosion meanscomprising:a plurality of non-explosion-proof electric motors for saidelectric drive motors and non-explosion-proof electric wiring for saidelectric wiring flexibly connecting each of said electric drive motorsto an electrical power source outside said explosive atmosphere; sealingmeans for enclosing said electric drive motors and said electric wiringfrom the explosive atmosphere; and pressurizing means for supplyingsufficient inert gas into said sealing means for surrounding said motorsand said wiring from a gas source outside said explosive atmosphere at apressure above said explosive atmosphere sequentially to reduce bypurging to an acceptable safe level the concentration of explosive gaswhich may have entered said sealing means, to maintain said sealingmeans at a pressure above said explosive atmosphere to prevent entry ofsaid explosive gas and to compensate for any leakage from said sealingmeans.
 2. An industrial robot for use in an atmosphere containing aninflammable or explosive gas, comprising:a robot assembly including astationary robot component and a plurality of movable robot components,at least a part of said stationary robot component and said movablerobot components having therein airtight chambers which communicate witheach other; communicating means for communicating the chambers with eachother; electric motors for driving and moving said movable robotcomponents, said motors disposed within at least two of said airtightchambers; a programmable controller for supplying electric power to saidmotors and for controlling said motors in accordance with apredetermined program, said controller disposed outside of saidatmosphere of inflammable or explosive gas and electrically connected tosaid motors through electric cables arranged in said airtight chambersand a conduit connected to said stationary robot component; and assupply means connected to at least one of said airtight chambers forsupplying inert gas to said chambers from a gas source outside saidatmosphere of inflammable or explosive gas at a pressure above thepressure of said atmosphere to compensate for any leakage from saidchambers and prevent the entrance of gases from said atmosphere to saidchambers while the inert gas being supplied surrounds the motors and thecables in said chambers and said conduit, whereby to obviate the needthat said motor and said wiring be heavy and explosion-proof so that themovable robot components may be compact and lightweight.
 3. The methodof electrically driving a plurality of relatively movable, compartmentedrobot parts in a hazardous environment by a lightweight,non-explosion-proof electric motor in the compartment of at least one ofthe robot parts being driven, characterized by the steps of:providingthat said compartment be substantially airtight when such compartmentedrobot parts are movable relative to each other; supplying sufficientinert gas to said compartment from a gas source outside said hazardousenvironment at a pressure above the pressure of said hazardousenvironment sequentially to reduce by purging to an acceptable level theconcentration of hazardous gas which may have entered said compartment,to maintain said compartment at a pressure above said hazardousenvironment to prevent entry of said hazardous environment and tocompensate for any leakage from said compartment while the inert gasbeing supplied surrounds the motor in said compartment, whereby toobviate the need that said motor be heavy and explosion-proof so thatthe robot parts may be compact and lightweight, wiring be heavy andexplosion-proof so that the robot parts may be further compact andlightweight.
 4. A compact, lightweight electrically driven robot adaptedfor use in a hazardous environment and to be controlled from outsidesaid hazardous environment, comprising:a base defining an airtight firstcompartment and having an outer stationary surface; a first drivemechanism including at least one non-explosion-proof electric motorreceived within the airtight first compartment; an arm assembly mountedfor movement relative to the base, and driven by the first drivemechanism, the arm assembly having an airtight second compartment; asecond drive mechanism including at least one non-explosion-proofelectric motor within the second compartment defined by the armassembly; a wrist mechanism mounted on the arm assembly and driven bythe second drive mechanism; a cable conduit extending from outside saidhazardous environment to the airtight first compartment; a plurality ofnon-explosion-proof cables housed within said cable conduit extendinginto said airtight first compartment, at least one of said cables beingflexible and connected to the first drive mechanism to operate theelectric motor thereof, and at least another of said cables beingflexible and extending from the airtight first compartment of the baseto the airtight second compartment of the arm assembly and beingconnected to the second drive mechanism to operate the electric motorthereof; said non-explosion-proof cables being sufficiently flexible toaccommodate the movement of said arm assembly relative to the base; apressurized gas supply for feeding pressurized gas into the airtightcompartments and into said cable conduit to provide pressurized gas thatsurrounds the electric motors in their respective compartments and thecables housed in the cable conduit, said gas supply being attached tothe outer surface of the base; sealing means cooperating between thebase, the arm assembly and the cable conduit to maintain thecompartments airtight and the pressurized gas surrounding thenon-explosion-proof electric motors and cables whereby the robot iscapable of operating in the hazardous environment; and communicatingmeans fluidly communicating the first and second compartments, saidpressurized gas supply feeding sufficient pressurized gas through saidcommunicating means to prevent gases from said hazardous environmentfrom entering said compartments and said cable conduit, whereby toobviate the need that said electric motors and said cables beexplosion-proof so that the robot may be compact and light-weight, saidgas supply being outside said cable conduit.
 5. A robot assemblycomprising:a stationary base defining a substantially airtight firstcompartment having an outer surface; an enclosure defining asubstantially airtight second compartment and mounted for rotationalmovement on the base; an arm assembly mounted for rotational movement onthe enclosure and defining at least one substantially airtightcompartment wherein the airtight compartments are successively mountedfor rotational movement relative to each other and fluid communicationtherebetween; a set of drive mechanisms, each set including at least oneelectric motor received in one or more of said compartments foreffecting rotational movement of one compartment relative to another; aconduit extending to the base and communicated to the first compartment,said conduit being attached to the outer surface of the base; a cablebundle extending from a robot controller, through the conduit and intothe airtight first compartment of the base, the cable bundle having atleast one cable connected to each set of drive mechanisms to operate theelectric motor therein, and said cable bundle including at least oneother cable that extends from the airtight first compartment of the baseinto the airtight second compartment and to each compartment in the armassembly for connection to the drive mechanism to operate the electricmotor thereof; communicating means for fluidly communicating the firstand second compartments, and the second and the at least one compartmentof the arm assembly successively; and a pressurized gas supply meansconnected to said base that feeds pressurized gas into the airtightfirst compartment of the base and thence into the conduit and theairtight second compartment of the enclosure and to the at least onecompartment of the arm assembly.
 6. The robot of claim 5 wherein the gassupply is outside said conduit.
 7. The method of electrically driving aplurality of relatively movable robot parts to manipulate said robotparts in a hazardous environment comprising the steps of:providing asubstantially airtight compartment in more than one of said robot partsso that such airtight compartments are movable relatively to each other;locating a lightweight non-explosion-proof motor for driving one of saidrobot parts in the airtight compartment next closest to the robot partbeing driven; supplying electrical power to said motor from a powersource outside said hazardous environment by means of flexible,lightweight, non-explosion-proof wiring so that said wiring can flexwhen said robot parts are moving relatively; housing said wiring in asubstantially airtight conduit from said power source outside saidhazardous environment which is in fluid flow communication with theairtight compartment in which said motor is located; and supplyingsufficient non-ignitable gas to said compartment and said conduit from agas source outside said hazardous environment at a pressure above thepressure of said hazardous environment to compensate for any leakagefrom said compartment and prevent the entrance of gases from saidhazardous environment to said compartment and said conduit while thenon-ignitable gas being supplied surrounds the motor in said compartmentand the wiring at said conduit, whereby to obviate the need that saidmotor and said wiring be heavy and explosion-proof so that the robotparts may be compact, lightweight and easily balanced; said step ofsupplying such non-ignitable gas being individually to said compartmentswhereby to individually pressurize each compartment containingelectrical equipment therein.
 8. An electric robot for use in ahazardous environment, including a base and an arm assembly supportedfor movement on said base, the base and the arm assembly forming aplurality of compartments including at least two relatively movablecompartments including electric motors and cables extending from outsidesaid hazardous environment to the electric motors, characterized in thatthe compartments are connected to each other by openings, means forpressurizing the compartments at a pressure above said hazardousenvironment, purging means for purging the compartments with clean airor an inert gas and a pressure regulator for regulating the pressurebetween predetermined limits, and sealing means arranged between thecompartments for withstanding the excess pressure.